when a layout changes, include change details in the layoutChange event

[heswell]

When a layout changes, a layout change event is triggered. This is handled by the Shell/layout management system , which persists the changed JSON representation of the UI.

Until now, the entire JSON structure of the UI has been persisted as one entity. We are moving to an approach that saves layouts individually, where the application level structure references those layouts rather than including them directly.

The layout change handling code needs to know whether any particular change is caused by a change at the application level (switching tabs, opening or closing a layout) or at the layout level (adding or moving a component within the layout, saving props on a component e.g sorting a table, applying a filter)

Modify the layout change callback to provide this information